## Q. 8.39

$\Delta U=q+w$

William Lan 2l
Posts: 73
Joined: Fri Sep 29, 2017 7:07 am

### Q. 8.39

How much heat is need to convert 80.0 g of ice 0.0 degrees C into liquid water at 20.0 degrees C?

Can someone give a conceptual explanation as well as the steps on approaching this problem?

Cooper1C
Posts: 50
Joined: Fri Sep 29, 2017 7:07 am

### Re: Q. 8.39

I would draw the phase change chart for water first. The first phase change is at 0 degrees and the second is at 100 degrees. If you start at 0 degrees (ice) and go to 20 degrees (liquid), you need to consider both the heat required to change ice to a liquid and the heat required to raise the temperature of the liquid from 0 degrees to 20 degrees.

torieoishi1A
Posts: 32
Joined: Sat Jul 22, 2017 3:00 am

### Re: Q. 8.39

Step 1: (melting the ice at 0 degrees C)
deltaH=amount of moles of water x the enthalpy of fusion at standard state
deltaH=(80g/18.02g/mol)x(6.01kJ/mol)=26.7 kJ
Step 2: (raising the temperature of the liquid water from 0 degrees C to 25 degrees C)
deltaH=m(specific heat capacity)(deltaT)
deltaH=(80g)(4.18J/Cg)(20C-0C)=6.69kJ
TotalHeatrequired=26/7kJ+6.69kJ=33.4kJ